Mystery of the silent woodlands: scientists are baffled as bird numbers plummet

It has hardly been noticed, but it is another sinister warning sign of a world going badly wrong. Populations of some of Britain's most attractive woodland birds are plummeting at a rate that threatens them with extinction, and nobody knows why.

It has hardly been noticed, but it is another sinister warning sign of a world going badly wrong. Populations of some of Britain's most attractive woodland birds are plummeting at a rate that threatens them with extinction, and nobody knows why.

Precipitous declines in the numbers of some species, of up to four-fifths, have been registered over the past 30 years, but scientists are just realising what is happening, and they have no simple explanation.

In its scale and its range, the phenomenon is one of the most ominous events in the natural history of Britain over the past half-century. Perversely, the decline comes at a time when Britain is planting more woodlands than ever, and forest management has never been more sympathetic to wildlife conservation.

About a dozen species of small birds that have flitted through our woodlands for thousands of years are suddenly in serious trouble. This may be associated with climate change, linked to the damage that excess deer numbers are doing to the undergrowth in woodlands, or in some cases, linked to trouble for birds on migration routes to and from Africa.

The endangered species are less familiar than common garden visitors such as robins and blackbirds, which is perhaps why their disappearance has taken longer to register. But now a study, appearing next month, makes the picture clear for the first time.

It shows that five of the species - the spotted flycatcher, the lesser spotted woodpecker, the lesser whitethroat, the lesser redpoll and the tree pipit - plunged by more than three-quarters between 1966 and 1999, and continues to decline.

The population of the spotted flycatcher fell by no less than 85 per cent, and that of the lesser spotted woodpecker by 81 per cent. Another five species - the willow tit, the marsh tit, the woodcock, the dunnock or hedge sparrow and the willow warbler - fell by between half and three-quarters, and two more species, the songthrush and the bullfinch, fell by nearly a half.

Yet another group, for which there are no reliable numerical figures, is nevertheless known to have fallen significantly in either numbers or in range, or in both. These include the long-eared owl, the hawfinch and the nightingale.

In southern England, where the situation is worst, some of these species have virtually disappeared. "These birds are falling off the radar in a quite catastrophic way and we have no real idea why," said Graham Appleton of the British Trust for Ornithology (BTO), Britain's leading bird research organisation. Three of its researchers, Rob Fuller, David Noble and Des Vanhinsbergh, produced the study with Ken Smith, a researcher from the Royal Society for the Protection of Birds.

The most puzzling and perhaps most worrying aspect of the woodland bird decline, apart from its remarkable scale, is that there is no obvious single cause, as there has been with the dramatic and well-known decline over the past 30 years of British birds on farmland.

Species of the fields such as the skylark, the grey partridge, the corn bunting and the turtle dove have also dropped enormously in numbers, but the reason is well-known, the range of new agricultural practices that came in with the intensive farming revolution.

Turning these declines around by more wildlife-friendly farming methods is now official government policy, and may well eventually succeed.

But the difficulty with addressing the woodland bird decline is that there is no obvious simple reason for it, and thus no obvious simple solution.

In their study, which will be published in the March edition of the journal British Birds, the researchers offer seven possible causes which may be behind the declines. They are:

* Pressures on migrant birds during migration, or on their wintering grounds in Africa;

* Climate change in Britain itself, especially changes in the timing of the emergence of insects used as food, and the drying-out of woodlands;

* Reduction in the actual numbers of insects and other invertebrates;

* Impacts of land use on woodland edges and on habitats outside woodland;

* Reduced management of lowland woodland;

* Intensified habitat modification by deer, which eat the woodland bushes, shrubs and grasses, and stop regeneration of trees, reducing nesting areas and insect populations;

* New pressure on nests and young birds from predators, such as grey squirrels, members of the crow family, and great spotted woodpeckers.

But at present, these possibilities are speculative, and the true causes of an enormous change in Britain's natural environment remain a mystery.

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